1. Field of the Invention
The present invention relates to a process for the transalkylation of nuclear methylated phenols into o-cresol in the liquid or gaseous phase, whereby particularly 2,6-dimethyphenol or a mixture of nuclear methylated phenols obtained, for example, as a residue in the case of an o-cresol synthesis, may be used as a starting material.
2. Description of the Prior Art
The synthesis residue obtained in the catalytic synthesis of o-cresol from phenol and methanol, which for the greatest part consists of 2,6-dimethylphenol (cf. German AS No. 1,256,755), frequently represents an undesirable and low grade by-product. The conversion into other valuable products, especially into o-cresol, which is needed for the production of herbicides in an increasing measure, is very valuable for economic reasons.
The isomerization and disproportionation of alkyl phenols in the liquid phase and gaseous phase have been known. However, the processes described hitherto were always based on the simultaneous use of catalysts. Thus oxidic catalysts, such as aluminum oxide, silicon-aluminum oxide as well as mixtures of silicon oxide with zirconium oxide or beryllium oxide, etc. are listed in several publications including German Patent No. 874,911; German Patent No. 1,014,550; German OD 1,956,383; U.S. Pat. No. 2,553,538; and British Patent No. 1,232,027. In all these cases, the reaction is not specific for o-cresol, but a mixture of numerous components is always obtained. Furthermore, in German OS No. 1,813,647, the use of an aluminum phenolate catalyst is described in the liquid phase reaction of a mixture of phenol and di-, tri- and polymethylphenols which, however, also only produces a partial conversion to o-cresol.